Stellar and Planetary Characterization of the Ross 128 Exoplanetary System from APOGEE Spectra

Diogo Souto, Cayman T. Unterborn, Verne V. Smith, Katia Cunha, Johanna Teske, Kevin Covey, Bárbara Rojas-Ayala, D. A. García-Hernández, Keivan Stassun, Olga Zamora, Thomas Masseron, J. A. Johnson (+5 others)
2018 Astrophysical Journal Letters  
The first detailed chemical abundance analysis of the M dwarf (M4.0) exoplanet-hosting star Ross 128 is presented here, based upon near-infrared (1.5--1.7 ) high-resolution (R∼22,500) spectra from the SDSS-APOGEE survey. We determined precise atmospheric parameters T_ eff=3231±100K, logg=4.96±0.11 dex and chemical abundances of eight elements (C, O, Mg, Al, K, Ca, Ti, and Fe), finding Ross 128 to have near solar metallicity ([Fe/H] = +0.03±0.09 dex). The derived results were obtained via
more » ... l synthesis (1-D LTE) adopting both MARCS and PHOENIX model atmospheres; stellar parameters and chemical abundances derived from the different adopted models do not show significant offsets. Mass-radius modeling of Ross 128b indicate that it lies below the pure rock composition curve, suggesting that it contains a mixture of rock and iron, with the relative amounts of each set by the ratio of Fe/Mg. If Ross 128b formed with a sub-solar Si/Mg ratio, and assuming the planet's composition matches that of the host-star, it likely has a larger core size relative to the Earth. The derived planetary parameters -- insolation flux (S_ Earth=1.79±0.26) and equilibrium temperature (T_ eq=294±10K) -- support previous findings that Ross 128b is a temperate exoplanet in the inner edge of the habitable zone.
doi:10.3847/2041-8213/aac896 fatcat:yaovkhatsjgs7pfqhm7vlbwtpi